diff --git a/internal/core/adt/composite.go b/internal/core/adt/composite.go
index 49995be..4ffc567 100644
--- a/internal/core/adt/composite.go
+++ b/internal/core/adt/composite.go
@@ -265,6 +265,25 @@
 	Finalized
 )
 
+func (s VertexStatus) String() string {
+	switch s {
+	case Unprocessed:
+		return "unprocessed"
+	case Evaluating:
+		return "evaluating"
+	case Partial:
+		return "partial"
+	case AllArcs:
+		return "allarcs"
+	case EvaluatingArcs:
+		return "evaluatingArcs"
+	case Finalized:
+		return "finalized"
+	default:
+		return "unknown"
+	}
+}
+
 func (v *Vertex) Status() VertexStatus {
 	if v.EvalCount > 0 {
 		return EvaluatingArcs
diff --git a/internal/core/adt/eval.go b/internal/core/adt/eval.go
index 806797f..b00b0b0 100644
--- a/internal/core/adt/eval.go
+++ b/internal/core/adt/eval.go
@@ -164,7 +164,7 @@
 				return &w
 			}
 		}
-		panic("nil value")
+		Assertf(false, "no BaseValue: state: %v; requested: %v", v.status, state)
 	}
 
 	if v.status < Finalized && v.state != nil {
@@ -180,15 +180,17 @@
 func (e *Unifier) Unify(c *OpContext, v *Vertex, state VertexStatus) {
 	// defer c.PopVertex(c.PushVertex(v))
 
+	// Ensure a node will always have a nodeContext after calling Unify if it is
+	// not yet Finalized.
+	n := v.getNodeContext(c)
+	defer v.freeNode(n)
+
 	if state <= v.Status() {
 		if v.Status() != Partial && state != Partial {
 			return
 		}
 	}
 
-	n := v.getNodeContext(c)
-	defer v.freeNode(n)
-
 	switch v.Status() {
 	case Evaluating:
 		return